l16 - design for assembly

8/7/2019 L16 - Design for Assembly

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MECH152-L16(1.0) - 1

Design forManufacturing and Assembly

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Handle

Join

Insert

Fasten

Inspect

AssemblyManufacture

Shapeforming

Handle

Primarymanufacturing

Shape forming

Inspect

Shapechange

Handle

Secondarymanufacturing

Machining

Inspect

Finish

Handle

Tertiarymanufacturing

Coating,treatment

Inspect

Assembly


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Assembly Processes Joining

Welding, brazing, soldering Riveting http://www.youtube.com/watch?v=l0E7SqOm1sA&feature=related

http://www.youtube.com/watch?v=xTZAucoSymk&feature=fvw

Inserting

Pin, keys, locators, etc (transitional orinterference fitting)http://www.youtube.com/watch?v=uhvQfZf6BPI&feature=related ;

Fastening Bolts and nuts Pressing

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Taxonomy of Assembly Operations

Electronic assemblyWiring 27%SMT 15%Soldering 12%Through hole insertion 7%

Cabling 5%Cleaning 4%Miscellaneous 30%

Mechanical assemblyFastening by screw

or bolt 38%Riveting 26%Pressing 6%

Miscellaneous 30%

http://www.youtube.com/watch?v=tS3NKSO6HJE&feature=related


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Economic SignificanceOther Production

47%Assemblyoperations 53%

Mating , joining50%

Feeding, handling, supervision,adjustment, inspection 50%

Total time inproduction

Materials and other production80%

Assembly

20%

Setup

12%

IntermediateAssembly

24%

FinalAssembly

24%

Support including qualitymanagement, design, facility, etc.

20%

Total unitproduction cost

MECH152-L16(1.0) - 6

Types of Assembly Manual assembly Assembly with

automation support Special purpose

assembly machines

Programmable/flexibleassembly machines

Important to achieveline balancing


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Objectives of DFMA Design rationalization and parts reduction

Modular design Parts and system interchangability and

standardization Process plan rationalization

Adapting optimized manufacturing process flow

Integrated design, manufacturing and measurement Enhanced assembly procedure and measurement

RATIONALIZATION OF PRODUCT DESIGN!

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Benefits of DFMA Average parts count reduction -

46% Average assembly cost

reduction - 47% Product cost reduction - 15%

Reduction in parts related costs Assembly tooling cost reduced Product introduction lead time

reduced Product reliability improved

Reducing the number of parts

Optimising manufacturingprocesses

Simplifying parts handling Improving product

assembly


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Assembly Relationship Assembly relationship can be represented by

entity-relationship diagram . Entity is a component Relationship is the functional relationship

and include information on the assembly. Inassembly analysis, this is called the liaisondiagram.

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Entity Relationship Diagram

Systemlevel

Componentlevel

Entity Relationship EntityDatabase

Database

Knowledge base

Case 1 - Sub-assembly levelE1 - power plugE2 cable cordR1 - power transmission,

red wire to the live pinblue wire to the neutral pingreen wire to the ground pincable cord fixed by cord grip to base

E1

E2R1


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Example - PlugComponent

IDComponent

nameFunctionalattributes

Matingcomponent

PLUG-1 cover housing base, cover screw

PLUG-2 ground pin safety base, fuse clip

PLUG-3 neutral pin powertransmission, 13A

base

PLUG-4 live pin powertransmission, 13A

base, fuse

PLUG-5 fuse clip fuse location ground pin, fuse

PLUG-6 cord grip cable location base, cord grip screw

PLUG-7 fuse safety, 13A fuse clip, live pin

PLUG-8 base housing cover, cover screw,ground pin, neutralpin, live pin, cord gripscrew, cover screw

P LUG-9 x 2 co rd grip screws cab le gripin g b ase, co rd grip

PLUG-10 cover screw housing assembly base, cover

Note: The wire gripping screwsare assumed to be part of the pinsub-assembly and are notincluded in the parts list

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Entity Relationship DiagramP1 (cover)

P8 (base)

P10 (cover screw)P9 (cord

grip screws)

P4 (live pin)P6 (cord grip)

P2 (ground pin) P3 (neutral pin)

P5 (fuse clip) P7 (fuse)

F

I

F

I

I

II

I

I

I

I

J


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Assembly Sequence Analysis Assembly drawing and part list, parts

drawing Generate E-R diagram Assign precedence and follower

relationship Generate precedence order graph (assembly

sequence graph) Checking and optimization

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Liaison Diagram Liaison diagram similar to ER diagram Build relationship between entities and

check all possibilities for precedence Consider the feasible ones


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Liaison Sequence Diagram Each row contains one or more state elements containing empty or filled-in

cells. Each state corresponds to a feasible subassembly or as many as two feasible

subassemblies. Each cell in a state corresponds to a liaison (relationship). Empty cells indicate

liaisons that have not been done, while filled-in cells indicate completedliaisons.

Each line between states is a transition, during which one or more liaisons aredone.

A path from the top state (no liaisons done) to the bottom state (all liaisonsdone) is a feasible liaison sequence. This diagram expresses two feasiblesequences.

Mechanical Assemblies: Their Design, Manufacture, an d Role in Product Development, D.E. WhitneyMechanical Assemblies: Their Design, Manufacture, and Role in P roduct Development, D.E. Whitney

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Example AutomobileAlternator

Sequence 1 Attractive single direction, no re-

orientation Hard to access the front housing,

difficult to tighten s crews for thebearing retainer

Sequence 2 Place rear housing in a fixture and adds

parts to it Front housing built as sub-assembly,

Fixture to grasp the retainer whilescrews are inserted

Requires two re-orientations, front housing and whole assembly

Undesirable re-orientating anunfastening subassembly

Mechanical Assemblies: Their Design, Manufacture, an d Role in Product Development, D.E. Whitney


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Example AutomobileAlternator

Sequence 3 Attractive single direction, no re-

orientation Differ from Sequence 1 with a front

housing built on separate fixture Additional fixture additional cost

Sequence 4 used by manufacturer Front housing built on separate fixture Manual inspection on the front housing

sub-assembly single direction, no re-orientation Not the best solution

Conclusion:Very hard to get an optimizedassembly sequence

Mechanical Assemblies: Their Design, Manufacture, an d Role in Product Development, D.E. Whitney

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DFA


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Basic Rules for DFA Design parts with end-to-end

symmetry or rotationalsymmetry about axis of insertion.

If parts are not symmetric, theyshould be obviously asymmetric

Avoid design that cause jamming or entanglement during

storage Avoid designing parts that havepoor handling too small, toolarge, sharp, splinter, delicate,slippery, flexible, etc.

Chapter 3, Product design of Manufacture and Assembly , Boothroydand Dewhurst

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Rules for Insertion & Fastening Design for smooth

insertion: Clearance fitwith no jamming; airrelief passage, chamfer,self-alignment

Chapter 3, Product design of Manufacture and Assembly , Boothroyd and Dewhurst


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Rules for Insertion & Fastening Standardization and

interchangeability:common parts,processes, and methodsacross product lines

Use Pyramid assembly best to assemble from

above


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Rules for Insertion & Fastening Avoid holding down

parts during placement

Design for consistentpart location on release

Choose low-costmechanical design



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Exampleshandling

self-alignment

insertion - chamfer

easy orientation andself-alignment

reduction of parts

asymmetric

non-tangling

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Examples


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Assembly EfficiencyBoothroyd and Dewhurst developed a

systematic method for DFA. a classification and coding system for manual

handling, insertion and fastening processes Assembly efficiency:

The number of parts in a product Ease of handling, insertion, and fastening of theparts

MECH152-L16(1.0) - 26

Example Power Saw



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Example Controller Assembly


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Controller Assembly Worksheet Analysis



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Design Changes and Savings

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Controller Assembly Redesign



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Additional Guidelines Avoid connections

Design for unrestricted

access


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Additional Guidelines Avoid adjustments

Use kinematic designprinciples



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Design for Assembly Automation

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Basic Considerations Design for ease of automatic feeding,

orienting, insertion, and assembly operation Rate (cost per unit time) for all operations

including the machine, the system, and the

down time should be known Cost of all the equipment Number of operators and technical staff Designed assembly rate


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ExampleFeeding equipment rate: R f =Cf Eo /(TP bSn)

Rf is the feeding equipment rate in cents/secondCf is the feeder cost converted to centsEo is the equipment overhead ratioT is the number of seconds per shift per monthPb is equipment payback in monthsSn is the number of shifts

Vibratory bowl feeder: http://www.youtube.com/watch?v=BY2Byhj0xbY&feature=relatedCf =$30,000 = 3,000,000 cents (including installation &

maintenance); E o = 2 (100% overhead); T = 864,000seconds/month (8 hour shift for 30 working days); P b = 18 months;Sn =2 (2 shifts)

Rf = 3,000,000 x 2 / 864,000 x 18 x 2 = 0.193 cents/secondMax. feeding rate = 10 parts/min. = 1/6 parts secondThe feeding cost / part = 6 x 0.193 cents = 1.1574 cents.

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Time Estimation Ergonomics study to support

time estimation Automation handling:

Geometric classification: Rotational: disc, short

cylinder, long cylinder Non-rotational: flat,

long, cubic Symmetry

Asymmetric projections,steps or chamfers

Feeding Thin edge shingling &

overlapping Flexible, tangling, sticky, light-

weight

Insertion Alignment and positioning Insertion path (vertical)



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Example


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Chapter 5, Prod uct design of Manufacture and Assembly , Boothroy d and Dewhurst


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Design Parts forFeeding and Orienting

Avoid designparts that willtangle, nest orshingle

Make partssymmetrical

For asymmetricparts, avoidslightasymmetry


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Additional Rules


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Example


Snap-fit

Me-Mo Modular Cellphone Design

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Capitalize on Material Properties Built-in spring

Part integration pressed,molded, or extruded parts, -sheet metal, plasticshttp://plastics.tuthill.com/Products/Insert%20Molding/Insert%20molding.asp

http://www.engineer.gvsu.edu/vac/


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Stable Base Structure Minimize assembly set-up

proper orientation

Good ergonomics designfor assembly operation good visibility andreachability

Adopting standardizedfixtures and tools

MECH152-L16(1.0) - 46

Example


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l16 - design for assembly

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